I have been riding a Trek 8.3DS for about a year now and want to use it for a Spring Duathlon. I want to put some good road tires on it for the race (stock tires are 700x38). I was told I could go as narrow as 25 on the road tires. Do I need a different tube? I want a fast tire but don't want to risk excessive flats. I'm 6'-3" & about 215lbs. What advice would you all have for me?

ESM

If you go that small, you will need new tubes.

I'm your weight an ride on 700x25s. Properly inflated, you shouldn't have any pinch flats. I pump up to 100 psi.

However I wouldn't recommend anything less than 700x28s as those rims are pretty wide. Even with 28's, I'd recommend new tubes.

Check your rims,there should be a sticker that says something like "622x##" with the last number being your rim width. Compare it to this chart,that will tell you how narrow of a tire will fit.

Thank you JerrySTL & dynaryder!

I'm also 6.3 at 280. I run 28's Vittoria Rubino with undersize tube. Riding everywhere and no flats yet on this setup in the last 2 years and few k miles.